1. Field of the Invention
The present invention relates to air conditioning apparatus in an air conditioning system for use in a vehicle in which an air conditioning amplifier unit (a master station) is connected to one or more door actuators (slave stations) through a single communication line and a single power source line to provide an LAN (Local Area Network) system, thereby controlling the angle of opening of a plurality of doors.
2. Description of the Related Art
Conventionally, as air conditioning apparatus in an air conditioning system for use in a vehicle, for example, as disclosed in Japanese Patent Publication No. Hei. 6-8746, there is known air conditioning apparatus in which actuator drive circuits respectively for driving respective door actuators are incorporated into an air conditioning amplifier unit, and the actuators respectively for an air mix door, for a mode door, and for an intake door are connected to the drive circuits by harnesses.
However, in the above-mentioned conventional air conditioning apparatus in an air conditioning system for use in a vehicle, the drive circuits and their respective door actuators are connected together through five to nine harnesses, so that the number and weight of the harnesses are large. Also, the door actuators vary in type such as a potentiometer system, an encoder type, and the like, which makes it impossible to mass produce the door actuators. Further, since the actuator drive circuits are incorporated into the air conditioning amplifier unit, the amplifier becomes large in size and the load of the microcomputer also becomes large.
Here, as means for solving these problems, there is known a method in which an air conditioning amplifier unit is connected to a plurality of door actuators by a single communication line to thereby provide an LAN system.
That is, employment of the LAN system can reduce the number of harnesses used, can integrate the actuators, and can realize a compact amplifier, with the result that there can be provided excellent advantages, that is, the weight reduction of the system as well as the reduction of the system cost.
However, when employing the LAN system instead of the current system, there are still left the following problems to be solved.
In the current system, if the target value of a fan motor voltage is equal to or higher than 8.5 V during the operation of the mode door or during the full hot side operation of the air mix door in a bent mode, then the maximum voltage value of the fan motor voltage is limited to 8.5 V, that is, the maximum voltage of the fan motor to secure a torque used to operate the door is limited to this value.
However, when the LAN system is employed and thus the door opening angle data or the like are transmitted unilaterally from the amplifier through a single communication line to the actuators, it is impossible to judge, for example, whether the mode door is in operation or not and, therefore, even if the 8.5 V limit of the fan motor voltage is to be executed, the conditions for removal of the limits of the fan motor voltage cannot be detected and thus the fan motor voltage remains left at 8.5 V, which makes it inevitable to relinquish the 8.5 V limit.